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If* OO/IO BUREAU OF MINES 

IU y^^i* INFORMATION CIRCULAR/1990 



Slip-and-Fall Accidents During 
Equipment Maintenance in the 
Surface Mining Industry 



By Thomas J. Albin and W. P. Adams 




^ ^ \ u.s. BUREAU OF MINES 

o m. J a M r" 



80 



X 



o 



1910-1990 



\ years / THE MINERALS SOURCE 

**au of ^ 



Mission: As the Nation's principal conservation 
agency, the Department of the Interior has respon- 
sibility for most of our nationally-owned public 
lands and natural and cultural resources. This 
includes fostering wise use of our land and water 
resources, protecting our fish and wildlife, pre- 
serving the environmental and cultural values of 
our national parks and historical places, and pro- 
viding for the enjoyment of life through outdoor 
recreation. The Department assesses our energy 
and mineral resources and works to assure that 
their development is in the best interests of all 
our people. The Department also promotes the 
goals of the Take Pride in America campaign by 
encouraging stewardship and citizen responsibil- 
ity for the public lands and promoting citizen par- 
ticipation in their care. The Department also has 
a major responsibility for American Indian reser- 
vation communities and for people who live in 
Island Territories under U.S. Administration. 



Information Circular 9249 

* »■ 



Slip-and-Fall Accidents During 
Equipment Maintenance in the 
Surface Mining Industry 



By Thomas J. Albin and W. P. Adams 



UNITED STATES DEPARTMENT OF THE INTERIOR 
Manuel Lujan, Jr., Secretary 

BUREAU OF MINES 
T S Ary, Director 







O 



o 



Library of Congress Cataloging in Publication Data: 



Albin, Thomas J. 










Slip-and-fall accidents during equipment maintenance 
industry / by Thomas J. Albin and W. P. Adams. 


in the surface 


mining 


p. cm. - (Information circular / 


Bureau of Mines (1988) ; 9249) 




Bibliography: p. 10. 










Supt. of Docs, no.: I 28.27:9249. 








1. Mine accidents. 2. Mines 
supplies-Maintenance and repair. 3. 
Paul), 1961- . II. Title. III. Series: 
of Mines); 9249. 


and mineral resources-Equipment and 
Falls (Accidents) I. Adams, W. P. (Wayne 
Information circular (United States. Bureau 


TN295.U4 [TN311] 


622 s- 


-dc20 [622'.8] 


89-600171 


CIP 



CONTENTS 

Page 

Abstract 1 

Introduction 2 

Problem description 2 

Problem background 2 

Objectives 3 

Method 3 

Accident record analysis 3 

Assessment of worker behavior 5 

Mining machine access system analysis 5 

Results 6 

Direct worker behavior 6 

Machine access system design 8 

Workstation design 8 

Discussion 8 

Relative hazard of direct worker behavior and machine access system design 9 

Risk perception 9 

Summary and conclusions 10 

References 10 

Appendix A.-Sample calculations of relative risk ratios 12 

Appendix B.-Calculation of probability of slip-and-fall accident happening to individual during 40-year 

period 13 

ILLUSTRATION 

1. Example of machine access system scoring sheet 7 

TABLES 

1. Operational definitions for antecedent events to slip-and-fall accidents 4 

2. Listing of antecedent events, codes, and frequency noted in accident narratives 6 

3. Antecedent events associated with direct and indirect worker behavior 6 

4. Slip-and-fall accident location, proportion of total work time in location, and relative risk 8 

5. Machine access system ratings 8 

6. Antecedent events related to workstation design 8 

7. Relative risk ratios for direct worker behavior and access system elements 9 



SLIP-AND-FALL ACCIDENTS DURING EQUIPMENT MAINTENANCE 
IN THE SURFACE MINING INDUSTRY 



By Thomas J. Albin 1 and W. P. Adams 2 



ABSTRACT 

This U.S. Bureau of Mines report identifies potential causes of slip-and-fall accidents occurring during 
surface mine equipment maintenance and describes the relative roles of direct worker behavior and 
machine design. The relative roles of human behavior and machine design in the causation of slip-and- 
fall accidents were determined through analysis of accident records, observations of maintenance worker 
behavior, and evaluation of mine machinery. From these data, relative risk ratios were calculated. 
Behavior had a relative risk ratio of 1.5; machine design, specifically access systems design, had a relative 
risk ratio of 2.2. Of the access systems, ladders had the highest relative risk ratio, 7.0. This study 
suggests that accident intervention would be most profitably made in improving the design of systems 
used to access maintenance worker areas of mining equipment. 



'industrial engineer, Twin Cities Research Center, U.S. Bureau of Mines, Minneapolis, MN (now with 3M Company, St. Paul, MN). 
2 Mechanical engineer, Twin Cities Research Center, U.S. Bureau of Mines, Minneapolis, MN (now with University of Nebraska-Lincoln, 
Lincoln, NB). 



INTRODUCTION 



PROBLEM DESCRIPTION 

Recent research conducted by the U.S. Bureau of 
Mines has shown that accidents occurring during main- 
tenance of mining equipment constituted 34 pet of all 
surface mining accidents from 1978 to 1984 (i). 3 Does this 
mean that maintenance is more hazardous than other min- 
ing activity? During 1986, the only year for which demo- 
graphic data regarding miners are available, there were an 
estimated 27,864 maintenance workers in the surface 
mining industry (2-3). Although these workers accounted 
for only 6.7 pet of all hours worked, they were involved in 
16.8 pet of all surface mining accidents (4). Based on 
these estimates, it appears that maintenance is 2-1/2 times 
more hazardous than other surface mining activities. 

Contemporary mining equipment is quite large, and 
maintenance workers must move about on it to perform 
their jobs. A large part of their work is performed in the 
presence of fluids, fuels, and lubricants. Dusts, ore 
particles, and other associated debris may also degrade 
surface footing properties. All of these substances put 
maintenance workers at risk for slips and falls. Bureau 
research found that slip-and-fall accidents constitute 
approximately 20 pet of all surface mining maintenance 
accidents. 

Slip-and-fall accidents, as a group, are more severe than 
are other mining accidents. A standard definition of 
accident severity, as used by the U.S. Mine Safety and 
Health Administration (MSHA), is the sum of the lost 
workdays plus the statutory number of penalty days 
assessed to each accident plus one-half the restricted duty 
workdays. One study found the average accident severity 
for all surface mining accidents to be 18.5 days compared 
with 33 days for slip-and-fall accidents (5). Thus slips and 
falls, as 20 pet of all maintenance accidents with an 
average severity 1.8 times the average, account for 36 pet 
of all maintenance accident severity. 

Slips and falls are clearly an important safety problem 
that costs individuals and mine operating companies 
dearly. The individual endures both the economic and 
physical costs of the accident, while the operating company 
endures increased insurance costs and losses in produc- 
tivity. It has been estimated that the average direct cost 
per case of all surface mining accidents is $14,000 (<5). If 
the relationship between accident severity and accident 
cost is linear, then an average slip-and-fall accident has an 
associated cost 1.8 times the overall average, or $25,200. 
This estimate is based on (1) loss in personal income, (2) 
compensation of wages, (3) death and disability benefits, 
(4) medical costs, (5) postaccident losses as a result of 
fatality or amputation, and (6) investigation of a fatal 
accident (6). The estimate does not include the costs 
of (1) loss of life, (2) fines, (3) lawsuits, (4) loss of 

Italic numbers in parentheses refer to items in the list of references 
preceding the appendix at the end of this report. 



equipment, (5) productivity losses due to workplace dis- 
ruption, (6) productivity losses due to temporary or 
permanent shutdowns, (7) productivity losses due to 
inexperienced replacement workers, or (8) long-term 
followup medical or rehabilitation treatment (6). 

The expected loss to a mining operator in a given time 
period can be estimated. During the first 6 months of 
1987, individuals employed in all sectors of surface mining 
operations, including coal, metal-nonmetal, and sand and 
gravel, with their associated plants and mills, worked a 
total of 398,179,605 h (7). During the same time period, 
1,163 slip-and-fall accidents occurred in these same 
operations (7). The expected incidence rate of slip- and- fall 
accidents per any given unit of time may be obtained from 
these data by division. It is the usual practice to base the 
incidence rate on the number of accidents per 100 work 
years, where a work year is defined as 2,000 h worked (one 
full-time equivalent) (7). Using this method, the expected 
incidence rate of slip-and-fall accidents in surface mining 
is 0.58 incidents per year per 100 full-time equivalents. 
(An alternative method for estimating incidence rates is 
described in reference 8.) The minimal expected cost of 
a slip-and-fall accident per 100 full-time equivalents is the 
product of the probability of a slip-and-fall accident (0.58), 
times the linearly estimated cost of a slip-and-fall accident 
($25,200), or $14,616. Thus, each surface mining operation 
should expect to incur approximately $15,000 in costs be- 
cause of slip-and-fall accidents per 100 full-time employees 
annually. 

This $15,000 cost figure can be used to "bench mark" 
intervention efforts aimed at preventing or decreasing the 
rate of slip-and-fall accidents. As an example, assume a 
mine with 100 full-time employees is contemplating spend- 
ing $20,000 in permanent improvements that would de- 
crease slip-and-fall accidents by 50 pet. This is an initial 
investment of $20,000 and a reduced expected annual cost 
of $7,500 (15,000 x 0.5). The expected payback period is 
2.67 years, calculated by dividing $20,000 by $7,500 per 
year (9). 

However, this example assumes that the miner has 
some knowledge of the causes of slip-and-fall accidents 
prior to addressing them, knowledge of the effect on the 
slip-and-fall incidence rate of remediating them once they 
are identified, and an idea of the cost of implementing the 
remediative measures. While the last might be estimated 
with accuracy, the first two are less well studied in surface 
mining. 

PROBLEM BACKGROUND 

Remediation of the causes of slip-and-fall accidents re- 
quires knowledge of the kinds of causes and their nature. 
In a general discussion of accident safety, two diametrically 
opposed explanations of accident causation are given. The 
first of these is that "stupid, careless, negligent people are 



the cause of 90 pet of all accidents and that the tools, 
machinery, or processes should not even be considered as 
being primary potential causes" (11). The other extreme 
explanation blames poorly designed products as the cause 
of accidents. The belief is that products should be so 
designed that, even in the presence of untrained careless 
persons, the product will have human fail-safe procedures 
features that will provide protection for persons from their 
own errors and negligence (10). While these two oppo- 
sites are recognized as extremes, they serve a heuristic 
purpose: To what extent are individual behavior and 
machine design involved as risk factors in slip-and-fall 
accidents in surface mining maintenance? 

A study done by MSHA in 1985 analyzing ladder falls 
from off-road haul trucks stated that "safe ladder systems 
are needed to prevent men from falling; however, in- 
sufficient training and unsafe work practices appear to be 
major causes of injuries associated with haul truck ladder 
systems" (11). It is worth noting that the researchers were 
unable to classify 65 pet of the accidents as to probable 
cause. Unsafe work habits were defined in this study as 
(1) missing a step, (2) carrying articles, (3) jumping from 
the ladder, (4) catching clothing or ring on a step or 
handrail, (5) not using the handrail, (6) falling from a 
moving truck and, (7) facing away from the ladder. While 
the classification of some of these behaviors might be 
debated, the import remains, individuals engage in risky 
behavior in the job environment. 

Risk may be defined logically as the expected loss re- 
sultant from a chosen alternative behavior (12), and it may 
be further divided into objective and subjective risk that 
often differ (13). Objective risk is the verbally expressed 
level of risk, i.e., "it is unsafe to climb a ladder while 
carrying an object in my hands," versus the subjective risk 
assessment, i.e., "I've carried this part up this way a 
hundred times before without any problem." Behavior 
clearly plays a role in slip-and-fall accidents, and risk 
perception logically plays an important role in behavior. 

Previous work by the Bureau on slip-and-fall accidents 
during maintenance has focused on the design of access 
systems (such as ladders, steps and stairs, and walkways) 
for mining machines (14). Serious design problems, 
particularly the height of the first step off the ground, were 
identified and remediative devices were developed. 



Risk behaviors associated with slip-and-fall accidents 
are, currently, not well described. Some are well known, 
i.e., descending a ladder facing outwards, but there are 
likely others as yet unidentified. In addition, the risk 
associated with these behaviors has not been directly 
assessed. Similarly, machine design problems have typi- 
cally been ascribed to existing access systems, i.e., the 
height of the first ladder step above the ground, but it is 
not clear if other design problems exist. 

It is apparent that remediation of slip-and-fall accidents 
will be necessary. It is also apparent that both behavior, 
including risk perception, and machine design are probable 
causes of such accidents, but that their relative importance 
is unclear. It is important to understand their relative 
causal roles in order to develop effective remediation 
strategies that will prevent or decrease slip-and-fall 
accidents. 

OBJECTIVES 

This research is part of the Bureau's program to en- 
hance the health and safety of mine maintenance workers. 
There are two major objectives of this study. The first is 
to develop a description of antecedent events to slip-and- 
fall accidents that occur during the maintenance of surface 
mining equipment. The second is to determine the relative 
roles of behavior and machine design in slip-and-fall ac- 
cident causation. These objectives will be accomplished 
through analysis of accident record narratives and field 
data. 

The description of behavior included identification and 
description of specific risk behaviors, estimation of the 
proportion of all behavior that the identified risk behaviors 
constitute, and finally, empirical estimates of risk resultant 
to the behaviors. 

Machine design was assessed both by compliance of ac- 
cess system design with the guidelines for access systems 
of off-road equipment described in the Society of Automo- 
tive Engineers Standard SAE J 185 (15) and by the evalua- 
tion of sufficiency and adequacy of existing access systems 
as determined through the analysis of accident records. 
Empirical estimates of the relative risk of various access 
system elements were developed. 



METHOD 



ACCIDENT RECORD ANALYSIS 

Accident records, including a short narrative description 
of the accident, were obtained from the MSHA data base 
through use of the Bureau's Accident Data Analysis 
(ADA) program. These accident records were drawn from 
the surface mining industry, which includes coal, metal and 
nonmetal, and aggregate mines. All slip-and-fall accidents 
involving surface mine maintenance workers in the years 
1985, 1986, and the first half of 1987 were analyzed. These 



were the most recent data available at the time of compila- 
tion. A total of 1,381 accident records were obtained. 
Based on 1986 estimates (2-3), these records pertain to 
18,362 mines and 27,864 workers. 

The accident narratives were typically not prepared by 
the injured individual. They were most commonly prepar- 
ed by safety officers, next followed in frequency by 
foremen, and finally by the injured individuals. Some addi- 
tional caveats regarding the narratives should be noted. 
The narratives were prepared after the fact. As such, their 



accuracy and validity may be fairly questioned. First, it is 
conceivable, and even likely, that important causal factors 
have not been included in some of the narratives. Second, 
the reliability of the narratives may be questioned. Given 
the free-form nature of the narrative, an individual might 
note and report widely differing narratives of highly similar 
events. This problem is further complicated when many 
different individuals are reporting accidents. Nonetheless, 
these records do contain information that has an important 
heuristic value for future research. 

The narrative records were read and classified by a 
single rater (Adams) using a prepared list of operationally 



defined event codes. This rater is a graduate engineer 
with approximately 1-year's experience in human factors. 
In order to assess rater reliability, 100 accident narratives 
were randomly drawn and classified by a second rater 
( Albin). The codes for these 100 records were compared 
with the codes prepared by Adams. A coefficient of agree- 
ment (7(5) of 0.93 (p < O.'OOl) was obtained. 

Event codes and definitions were created for any events 
discovered in the course of analysis that did not fit events 
defined in the original list. The final list of events and 
their definitions are presented in table 1. 



Table 1 .-Operational definitions for antecedent events to slip-and-fall accidents 

Event Definition 

Ladder structural failure Ladcer component failed while in use. 

Slipped on ladder Individual slipped while on ladder. 

Ladder slipped or fell Portable ladder slipped or fell while in use. 

Handrail not used Individual did not use handrail while climbing ladder, stairs, etc. although hands 

were free. 
Carrying object while using ladder . . Individual carried object while climbing or descending ladder, so that hands 

were not free to grasp handrail. 

Handrail did not arrest Handrail friction was insufficient or excessive load on hand gripping rail. 

Fell from ladder Individual fell from ladder. 

Stepped off access system Individual slipped and fell while stepping from ladder, step, etc. to base 

surface. 
Siipped on surface Individual slipped on mud. ice. etc. while walking on parking lot, pitfloor, etc. (not 

incasing building floors). 
Unmarked hazard Unmarked or unguarded hazard, particularly holes in surface made by missing 

plates of deck grating. 

Tripped on uneven surface Indivic-al tripped on projection from surface. 

Tripped on grating Individual tripped when cleats of work boots were caught in grating. 

Siipped on debris Individual slipped on debris, scrap, ore. tools, etc. on surface. 

Siipped on spill Individual slipped on spilled substance, such as lubricant, coolant, water. 

Slipped on work surface Individual slipped on surface of work area (including building floors). 

Slipped on stairs or step Individual slipped or fell on stairs or step. 

Portable stairs moved Portable stairs moved while in use. 

Siipped off machine Individual slipped or fell from machine because of poor surface traction. 

Slipped on machine Individual slipped while on mobile or stationary machine and fell on machine. 

Slipped on machine access system . Individual slipped and fell while stepping onto ladder, step. etc. from base 

surface. 

Slipped on catwalk Individual slipped on walkway or catwaJk. 

Slipped on deck Individual slipped on deck of mobile or stationary machine. 

No escape route Escape route was not designed into system. 

Jumped Individual jumped from one location to another, as in jumping between 

machines or down from machines. 
Inadequate workstand Workstand did not have sufficient surface traction or was lacking a necessary 

component, such as a guardrail. 
No guardrail Individual fell off object, such as workstand or platform because guardrail was 

not in place. 

Guardrail structural failure Guardrail failed because of load. 

No toe rail Individual's foot slipped over edge or object, such as tool, dropped off because 

toe rail was not provided. 
Structural failure Failure of structural member not part of access system. Failure of structural 

member not designed for use as access system but being used for such is 

coded as inadequate workstand. 

Inadequate access design Access system not designed properly to enable adequate access to machine. 

Unexpected energy release Individual fell when unexpected energy was released, such as wrench slipping 

or rope breaking. 
Work boots not cleaned Individual slipped and fell because of decreased traction due to mud, oil, etc. 

on boots. 

Clothes caught on object Individual slipped and fell when clothes caught on object. 

Unknown Not enough information to classify. 

Access system not used Individual did not use access system although one was available. 

Knee gave way Individual's knee buckled causing slip and fall. 

Falling or raising object Accident caused by falling object, or while individual was raising object. 

Bumped head Accident caused by bump to head. 

Carried object Individual was carrying object in hands prior to accident. 



Coce 

10 

11 

12 

13 

14 

15 

16 

17. 33. 41 

20 . 

21 

22 

23 

24 

25 

26 

30. 32 . . 

31 

40 

42 

43 

44 

45 

46 

47 

50 

51 

52 

53 

54. 64 . . 

55 

60 

61 

63 

65 

66 

70 

71 

72 

73 



ASSESSMENT OF WORKER BEHAVIOR 

The analysis of accident narrative reports described in 
the section "Accident Record Analysis" was used to de- 
velop a list of direct worker behaviors that were antece- 
dent to slip-and-fall accidents. These behaviors include 
using a ladder while carrying an object in the hands; 
jumping from a machine; not using an access system when 
one is available; and not cleaning oil, mud, etc. off of work 
boots. 

For the field phase of the study, two researchers 
observed maintenance work activity for a combined 80 h 
of observation time. During this time, four maintenance 
workers were scheduled to be filmed while performing 
their normal duties for 2 h each on 2 separate days over a 
period of 4 days. Filming was done while maintenance 
personnel accessed front-end loaders, bulldozers, off-road 
haul trucks, road graders, power shovels, and various 
stationary machines such as crushers, etc. In actuality, 
much of the maintenance work observed during these 
filming periods took place in areas that were physically 
inaccessible to the camera. Consequently, only about 2 h 
film was gathered on each of the four individuals. One 
individual at a time was filmed, starting on the second and 
sixth hours of each shift in order to control for time 
effects. Both the days when filming occurred and the 
order of filming during the shift were randomly deter- 
mined for each individual. While the possibility of a 
Hawthorne effect exists, previous research has suggested 
that such behavior changes are transient and disappear 
after repeated observations (17). 

Behavioral samples were obtained by viewing randomly 
determined portions of 1 day's videotape of each of the 
four maintenance workers while they serviced mining 
equipment. The days used were randomly selected for 
each individual as follows. Each of the four selected tapes 
was numbered in sequence. The lengths of the selected 
videotapes, as indicated by the tape player's incremental 
counter, were added, in order of sequence, to generate 
a total tape length. A BASICA program was written to 
generate a list of 100 random numbers ranging between 
and 1. Each of these numbers was then multiplied by 
the total tape length to generate a point at which the ob- 
servation was to occur. The tape was then viewed at these 
points. A tally was made of all instances where one of the 
high-risk behaviors was observed. 

During each day that an individual maintenance worker 
was selected for filming, that individual was under continu- 
ous observation by an observer. The observer recorded 
information on the relative proportions of time that 
maintenance workers spent in various locations, including 
various access systems. These locations were (1) on a 
ladder, (2) on the ground, (3) on stairs, (4) stationary on 
a machine, (5) on a workstand, (6) climbing on a machine 



where no prepared access existed, (7) on a walkway, 
(8) operating a machine, and (9) miscellaneous. 

These worker location data were collected continuously 
on all four maintenance workers over the 4-day period 
using a systematic random sampling procedure (18) at 
10-min intervals after a randomly determined starting 
point. These data were recorded in a notebook. 

The objective of this phase of the study was to estimate 
two proportions: the proportion of high-risk behaviors and 
the proportion of time spent in various locations. The 
estimates of these proportions were accomplished via a 
work-sampling technique (18). This method may be used 
to estimate the precision of the estimate of a proportion 
using equation 1: 



N = (p' (1 - pO^/D 2 , 



(1) 



where N 
P' 



and 



D 



= number of samples required, 

= first-guess estimate of the proportion,' 

= z-score for any desired confidence 
interval, 

= desired precision of the estimate of the 
proportion, expressed as a decimal frac- 
tion and interpreted as the proportion 
plus or minus D pet. 



While z was specified prior to the study as 1.96, and 
time constraints suggested a maximum sample size, N, of 
100, the proportion of risk behaviors was unknown at the 
beginning of the study, resulting in an unknown degree 
of precision. It was decided to use a conservative pro- 
cedure (18) to estimate the precision for a sample size 
of 100 observations. This procedure consists of setting p' 
equal to 0.5 and solving equation 1 for D. Using this pro- 
cedure yielded a value of 0.09 for D. This was considered 
to be an acceptable level of precision, particularly as 
the true proportion was considered likely to be much less 
than 0.5, which would result in increased precision of the 
estimate with a sample size of 100. 

MINING MACHINE ACCESS SYSTEM ANALYSIS 

Access systems of mobile mine equipment were 
evaluated for new (1988) and older (pre- 1988) machinery. 
Access systems of the new machines were evaluated with 
the manufacturers' permission and cooperation at the 1988 
MINEXPO show in Chicago, IL. Of the new off-road 
machines examined, three were front-end loaders and two 
were trucks. These machines are a reasonable representa- 
tion of equipment that would be found in a surface mine, 
with the notable exception of power shovels. 



Of the older machines evaluated at a cooperating min- 
ing operation, two were front-end loaders and two were 
off-road haul trucks. All machines were evaluated for 
compliance with the recommended access system design 
guidelines published by SAE (15). Scoring sheets were 
constructed for this evaluation, which depicted different 
access system components and the relevant dimension lines 
of each. Each relevant dimension of the access system, 
e.g., ladder width, was given a letter code. The evaluator 
recorded the site of any particular access system 
component on the machine, e.g., cab access, and the 
measurements appropriate to that particular access system 
element by letter code on the sheet. A sample scoring 
sheet is shown in figure 1. 

Dimensions for each access system element were scored 
to indicate compliance with the SAE J185 standard. The 
SAE J185 standard gives minimum, maximum, and rec- 
ommended dimensions for each access system element. 
If the access system of a machine was within 10 pet, 
plus or minus, of the recommended dimension, it was 
given a score of 1. An access system element whose 
dimensions were between the maximum and minimum 
given in SAE J185 but not within a 10-pct range of the 
recommended dimension was given a score of 2. An 
access system element whose dimensions were outside the 
maximum or minimum values was given a score of 3. 
Each access system component was given a composite 
score, which was the arithmetic average of its subelements' 
scores, i.e., the score for a ladder would be the average of 
the score for step width, handrail diameter, etc. 

RESULTS 

A complete listing of antecedent events, their associated 
codes, and the frequency with which they were noted in 
the accident records is presented in table 2. The total 
number of events exceeds the number of accidents because 
some accidents had more than one antecedent event noted. 

Direct Worker Behavior 

Direct volitional behavior of the individual involved in an 
accident was noted in 8.9 pet of all accident narratives. 
These behaviors included descending a ladder facing 
outward; carrying an object while using a ladder; jumping 
from a machine; not cleaning mud, oil, etc. from work 
boots; or not using an access system when one is available. 

Using the random sampling procedure described in the 
"Methods" section, 100 observations were made of main- 
tenance workers' behavior while they were maintaining 
mining equipment. During these observations, six in- 
stances of direct, high-risk behaviors, such as jumping off 
the machine, were observed. Thus, the estimate of the 
proportion of high-risk behaviors, as calculated from 
equation 1, is 0.06, plus or minus 0.05. A summary of all 
behavioral data from both the accident records and field 
observations is presented in table 3. 

Table 3 indicates that an additional 237 accidents (17.2 
pet) had a possible behavioral component, although the 



behavior was not necessarily that of the injured individual. 
These events were unmarked hazards, such as removed 
floor plates, debris on surface, and spills on surface. 

Table 2.-Listing of antecedent events, codes, and 
frequency noted in accident narratives 

Event Code Frequency 

Slipped on surface 20 170 

Slipped off machine 40 170 

Unknown 65 141 

Slipped on spill 25 129 

Stepped off machine 41 116 

Tripped on uneven surface 22 104 

Unexpected energy release 60 97 

Slipped on machine 42 90 

Inadequate workstand 50 89 

Slipped on work surface 26 82 

Slipped on debris 24 73 

Carried object 73 62 

Slipped on step 32 55 

Slipped on stairs 30 53 

Jumped 47 51 

Fell from ladder 16 50 

Slipped on ladder 11 48 

Stepped off structure or equipment other 

than machine 33 39 

Ladder slipped or fell 12 38 

Access system not used 66 38 

Unmarked hazard 21 35 

Falling or raising object 71 34 

Other structural failure 54 32 

Knee gave way 70 27 

Work boots not cleaned 61 25 

Stepped on machine access system .... 43 22 

Stepped off ladder 17 12 

Slipped on catwalk 44 12 

Slipped on deck 45 9 

No guardrail 51 9 

Carrying object while using ladder 14 7 

Tripped on grating 23 6 

Portable stairs moved 31 6 

Guardrail structural failure 52 6 

Clothes caught on object 63 6 

Ladder structural failure 10 5 

Inadequate access design 55 4 

Bumped head 72 3 

Handrail not used 13 2 

Handrail did not arrest 15 2 

No escape route 46 2 

No toe rail 53 2 

Total structural failure 64 1 



Table 3.-Antecedent events associated with direct 
and indirect worker behavior 

Event Code Frequency 

Direct: 

Jumped 47 51 

Access system not used 66 38 

Work boots not cleaned 61 25 

Carried object while using ladder 14 7 

Handrail not used 13 2 

Total 123 

Indirect: 

Slipped on spill 25 129 

Slipped on debris 24 73 

Unmarked hazard 21 _35 

Total 237 



Model : 




Loc 



Loc 



Loc 



Loc: 



Loc 



Loc 



Loc 



A 


A . 


A 


A 


A 


A 


A 


R 


R 


R 


R 


R 


R 


R 


C. 


r. 


r. 


c 


r. 


C 


C 


n 


n 


n 


D 


n 








F 


v. 


F 


E 


E 


F, 


F 



Figure 1. -Example of machine access system scoring sheet (Loc = location). (Courtesy Society of Automotive Engineers (15)) 



Machine Access System Design 



Table 4.-Slip-and-fall accident location, proportion of 
total work time in location, and relative risk 



The accident narratives indicate that access system 
elements (ladders, steps and stairs, and walkways) were the 
location of 291 accidents (21.1 pet of total). Field data 
indicate that workers spend 10.8 pet of their total work 
time on ladders, steps and stairs, and walkways. A 
convenient way of evaluating the relative risk of access 
system elements is to divide the percentage total of all 
accidents that occur on an access system element by the 
percentage of total work time during which the worker is 
located on that element. The higher the obtained ratio, 
the more hazardous the access system element. Such an 
analysis is presented in table 4. This table incorporates the 
accident narrative data with the data obtained in the field 
regarding the location of the worker. Ladders, with a ratio 
of 6.1, and steps and stairs, with a ratio of 2.4, are the 
most hazardous of the access system elements. The cate- 
gories of surfaces and machines have been added to this 
table for completeness. 

Measurements were taken on the access systems of 
eight new machines at the 1988 MINEXPO in Chicago, 
IL. Three of these machines were front-end loaders and 
two were off-road haul trucks. Similar measurements of 
older machines were taken at a cooperating mining 
operation on two front-end loaders and two off-road haul 
trucks. These data are presented in table 5. There is a 
noticeable improvement in the design of the newer 
equipment access systems. The overall average rating for 
new machine access systems was 1.7 as compared with 2.0 
for older machines. Older truck ladders deviate the most 
from the SAE J 185 guidelines with an average of 2.6. 



Workstation Design 

Maintenance workers often gain access to the workplace 
through the use of workstands or other means of access 
that are not an integral part of the mining equipment. 
A common example is a stepladder. A number of such 
accidents where the workstand design appeared to be at 
fault were noted in the accident narratives. These 
incidents were grouped with other records where there 
were apparent design problems with the workstation. 
Three hundred instances of workstation design problems 
were noted in the accident narratives. These data are 
presented in table 6. 



Location Frequency 


Pet total 
accidents 


Pet total 
work time 


Ratio 


Access systems: 

Ladders 

Stairs and steps 
Walkways .... 

Surfaces 

Machines and all 
else 


160 

114 

12 

252 

843 


11.6 

8.3 

.9 

18.2 

61.0 


1.9 

3.5 

5.4 

38.9 

51.0 


6.1 

2.4 
.17 
.47 

1.20 


Table 5.-Machine i 


access system ratings 




Machine 


Ladders 


Walkways 


Handrails 


Average 


NEW 


Front-end loaders: 

A 

B 

C 


2 

2.1 

1.5 


1 
2 
1 


1.8 
2.7 
1.5 


1.6 
2.3 
1.4 


Average 


1.9 


1.3 


2.0 


1.8 


Trucks: 

D 

E 


1.5 
1.8 


1.3 
1.5 


1.7 
1.5 


1.5 
1.6 


Average 


1.7 


1.4 


1.6 


1.6 


Overall average 


1.8 


1.4 


1.8 


1.7 


OLDER 


Front-end loaders: 

F 

G 


1.6 
1.8 


2 
2 


NA 
1.9 


1.8 
1.9 


Average 


1.7 


2 


1.9 


1.9 


Trucks: 

H 

I 


2.5 
2.7 


1.7 
1 


2.7 
2 


2.3 

1.9 






Average 


2.6 


1.4 


2.4 


2.1 


Overall average 


2.2 


1.7 


2.2 


2.0 


NA Not available. 

Table 6.-Antecedent events related to workstation design 



Event Code Frequency 

Tripped on uneven surface 22 104 

Inadequate workstand 50 89 

Ladder slipped or fell 12 38 

Other structural failure 54 32 

No guardrail 51 9 

Guardrail structural failure 52 6 

Portable stairs moved 31 6 

Ladder structural failure 10 5 

Inadequate access design 55 4 

Handrail did not arrest 15 2 

No toe rail 53 2 

Total structural failure 64 1 

Total 298 



DISCUSSION 



This study sought to identify antecedent events to slip 
and fall accidents in order to develop a better under- 
standing of the causation of such accidents. In addition, it 
sought to describe the relative roles of worker behavior 
and machine design contributory to accidents. It was 
further hypothesized that the perception of risk would 



affect behavior. Data were collected from two different 
sources: reports of surface mining maintenance accidents 
and a field study of maintenance workers. 

There were three major findings in this study. First, 
analysis of the accident narratives showed that 286 acci- 
dents, or 20.7 pet of the total number of accidents studied, 



occurred on access system elements such as ladders, stairs 
and steps, and walkways. In contrast, workers spent only 
10.8 pet of their total work time on access system ele- 
ments. Second, a group of direct worker behaviors ante- 
cedent to slip-and-fall accidents was identified in the 
accident narratives. These direct behaviors were found in 
123 accident narratives, or 8.9 pet of the total number of 
accident reports. Field studies indicated that these 
behaviors constituted approximately 6 pet of all worker 
behaviors, plus or minus 5 pet. Third, older machines 
were ranked lower than new machines when measured 
against the SAE J 185 standards, with overall rankings of 
2.0 and 1.7, respectively. Ladders and handrails on older 
off-road haul trucks were particularly problematic. 

Finally, during the 80 h of observation, a single slipping 
accident was observed. This slip did not result in an injury 
and occurred on a fixed ladder. No direct behavior ante- 
cedents were observed prior to this incident. 

RELATIVE HAZARD OF DIRECT WORKER 

BEHAVIOR AND MACHINE ACCESS 

SYSTEM DESIGN 

In order to discuss the relative roles of direct worker 
behavior and machine design in the causation of main- 
tenance slip-and-fall accidents, a mutual basis of com- 
parison between these two classes of antecedent events 
must be established. The method used in this report is to 
calculate relative risk ratios. Relative risk ratios compare 
the rates of occurrence of an accident in one location or 
category with the rate of occurrence of similar accidents 
elsewhere. A relative risk ratio greater than 1 indicates a 
higher degree of risk associated with that given category. 
The general formula for relative risk ratios is given in 
equation 2 (19). 



RR = 



(AcC/hC) 



(TAc - AcC)/Th - hC) 



(2) 



where RR = relative risk, 

AcC = accidents associated with category, 

hC = hours worked in category, 

TAc = total number of accidents, 

and Th = total hours worked. 

(The term "category," as used in this equation, refers to 
location or the type of behavior associated with the acci- 
dent and hours worked terms.) Conceptually, there is no 
difference between the proportion of hours worked and 
the number of hours worked. The field estimates of the 
proportion of work time spent in various locations or 
behaviors was substituted for the number of work hours; 
the total work hours is then equal to unity. 



The first comparison made was between direct behavior 
and use of access system elements. Direct behavior has a 
relative risk ratio of 1.5, while access systems have a rela- 
tive risk ratio of 2.2. These ratios are presented in ta- 
ble 7; the calculation of all relative risk ratios is included 
in appendix A. Access systems are relatively more hazard- 
ous than direct behavior. This effect is maintained when 
the overlap cases are eliminated from the calculation of 
the relative risk ratios. Based on the accident narratives, 
there is an overlap of 18 cases between the 2 sets of ante- 
cedent events: direct behavior and access system elements. 
If these cases are eliminated, the relative risk ratios for be- 
havior and access systems are 1.3 and 2.0, respectively. 

Table 7.-Relative risk ratios for direct worker 
behavior and access system elements 

Category Risk ratio 

Direct behavior 1.5 

Access systems 2.2 

Direct behavior 1 1.3 

Access systems 1 2.0 

Individual access system elements: 

Ladders 6.8 

Stairs and steps 2.5 

Walkways .2 

'Overlap cases eliminated. 

The preliminary ratios in table 4 suggest that some ac- 
cess elements, particularly ladders, are more hazardous 
than others. Accordingly, relative risk ratios were cal- 
culated for individual access system elements. These ratios 
are also presented in table 7. Ladders have a very high 
relative risk ratio of 6.8, stairs and steps have a high ratio 
of 2.5, and walkways have a very low ratio of 0.2. The 
relative risk ratios confirm the preliminary estimates of 
the relative hazards of access system elements made in 
table 4. 

The greatest hazard antecedent to slip-and-fall accidents 
is apparently the access systems, particularly ladders. 
Reference to table 5 shows that, although improvement 
has been noted, ladders are tied for the worst overall 
ranking in terms of compliance with SAE J185 off-road 
access system standards. Commonly noted ladder defici- 
encies were the height of the first step above the ground 
and unequal spacing of ladder rungs. 

RISK PERCEPTION 

The concept of subjective risk was introduced earlier in 
this report. Subjective risk is defined as the individual's 
experience of the hazard level associated with some behav- 
ior. The field data gathered on worker behavior give some 
understanding of the subjective experience of risk asso- 
ciated with behavior. During the maintenance of the min- 
ing equipment, six high-risk behaviors were observed dur- 
ing a 105-min observation period. The individuals were 
engaging in identified risk behaviors at a rate of one 
behavior every 17.5 min. None of these behaviors resulted 
in an accident. 



10 



During the collection of field data, one slipping incident 
was observed in approximately 80 h. This incident did not 
result in an injury. 

Earlier, the incidence rate of slip-and-fall accidents was 
estimated as 0.58 per 100 work years for all surface mine 
workers. Using the same method, the incidence rate of 
slip-and-fall accidents for maintenance workers is esti- 
mated as 1.98 per 100 work years. 

An individual worker's subjective risk experience with 
regard to hazardous behaviors would be this: A minor, 
non-injurious slip might be expected, on average, after 
enough time had elapsed for the occurrence of 274 haz- 
ardous, or risk associated behaviors. An accident has a 
probability of occurrence of 0.019 per work year. Thus, 
using a binomial estimate, there is about an even chance 



(p = 0.46) that a worker could work 40 years without ex- 
periencing a slip-and-fall accident. (The calculations for 
this probability are shown in appendix B.) It should now 
be apparent that the subjective level of risk of engaging in 
risk behavior is, justifiably, quite low. 

Similar arguments can be made for estimation of the 
subjective appreciation of the risk of using access systems. 
The estimated incidence rate of slip-and-fall accidents 
while using access systems is 0.46 per 100 work years. 
(Calculations are shown in appendix B.) If this rate is 
converted to an annual binomial probability of injury while 
using an access system of 0.004, the probability of working 
for 40 years without experiencing a slip-and-fall injury 
while using an access system is 0.84. 



SUMMARY AND CONCLUSIONS 



The Bureau studied slip-and-fall accidents that occurred 
during surface mining maintenance. A list of antecedent 
events to slip-and-fall accidents was generated from analy- 
sis of slip-and-fall accident narratives. 

Two main variables were studied as they related to slip- 
and-fall accidents during surface mining maintenance. 
These variables are the direct behavior of the individuals 
involved in the accident and the design of the access 
systems. The use of access systems was found to have a 
higher relative risk ratio than the direct, hazardous 
behaviors identified from the analysis of the narratives. 
Ladders were identified as the most hazardous of access 
systems. Improvement in the compliance of new equip- 
ment access systems with SAE J 185 guidelines was noted, 
but the access systems of older equipment, particularly 
off-road haul truck ladders, are still problematic. 
Subjective risk values were estimated for maintenance 
workers; the obtained values were quite low, suggesting 
that individuals will routinely engage in risk behavior 
without significant expectation of injury. 



While the probability of a slip-and-fall injury is small 
for any individual maintenance worker, it is cumulative for 
a group. The probability of a maintenance worker sustain- 
ing a slip-and-fall injury in a company with five mainten- 
ance workers is 0.095 during any year. Thus, it is probably 
more reasonable for a company to be more sensitive to 
accident risk than an individual because the expectation of 
loss is greater. 

Given that a company is more likely to be sensitive to 
the risk of slip-and-fall accidents, what strategies should be 
taken to improve slip-and-fall safety? The first priority, 
based on the findings of this study, would be to improve 
the quality of access system elements, particularly ladders. 
A reasonable approach might be to bring them into com- 
pliance with the SAE J185 guidelines. The second priority 
would be to make an effort to change the subjective risk 
perception of the maintenance workers. Training pro- 
grams have been described (20) that effectively teach 
workers to recognize hazards and to change their behavior 
accordingly. 



REFERENCES 



1. Long, D. A. An Analysis of Off-Highway Haulage Truck Main- 
tenance and Repair Accidents, 1978-84. BuMines IC 9139, 1987, 15 pp. 

2. Butani, S. J., and A. M. Bartholomew. Characterization of the 
1986 Coal Mining Workforce. BuMines IC 9192, 1988, 76 pp. 

3. . Characterization of the 1986 Metal and Nonmetal 

Workforce. BuMines IC 9193, 1988, 69 pp. 

4. U.S. Department of Labor. Mine Injuries and Worktime, 
Quarterly. Closeout Ed., 1986, 31 pp. 

5. Albin, T. J. Bureau Research in Human Factors Applied to 
Recent Accident Experience in the North-Central Region. Pres. at 
MSHA-IL Dep. Mines & Miner.-IL Assoc. Aggregate Prod. Saf. Conf., 
Feb. 24, 1988, 6 pp.; available from T. J. Smith, Twin Cities Res. Cent., 
BuMines, Minneapolis, MN. 

6. Chi, D. N. H., and B. J. Hamilton. Trends in Mining Accidents 
and Their Costs (1975-1984). Pres. at 19th Int. Symp. on Appl. of 
Comput. Methods in Miner. Ind., University Park, PA, Apr. 14-18, 1986, 
14 pp.; available from Librarian, Twin Cities Res. Cent., BuMines, 
Minneapolis, MN. 



7. U.S. Department of Labor. Mine Injuries and Worktime, Quar- 
terly. Jan.-June 1987, 33 pp. 

8. Kogut, J. An Empirical Bayes Methodology for Accident Risk 
Estimation and Incidence Rate Comparison. MSHA, Health and Saf. 
Anal. Cent., Denver, CO, 1982, 93 pp. 

9. Lutz, R P. Discounted Cash Flow Techniques. Ch. in Hand- 
book of Industrial Engineering, ed. by G. Salvendy. Wiley, 1984, 
pp. 9.3.1-9.3.17. 

10. Miller, J. M. The Management of Occupational Safety. Ch. in 
Handbook of Industrial Engineering, ed. by G. Salvendy. Wiley, 1984, 
pp. 6.14.1-6.14.18. 

11. Quisenberry, S. Injuries Associated With Truck Ladders. MSHA 
Health and Saf. Anal. Cent., Denver, CO, 1982, 36 pp. 

12. Oppe, S. The Concept of Risk: A Decision Theoretic Approach. 
Ergonomics, v. 31, 1988, pp. 435^40. 

13. Howarth, C. I. The Relationship Between Objective Risk, Subjec- 
tive Risk, and Behavior. Ergonomics, v. 31, 1988, pp. 527-535. 



11 



14. Long, D. A. Improved Personnel Access for Surface Mining 
Equipment. BuMines IC 8983, 1984, 20 pp. 

15. Society of Automotive Engineers. Access Systems for Off-Road 
Machines. SAE J185 (Aug85) in On-Highway Vehicles and Off- 
Highway Machinery. SAE Handbook, v. 4, 1987, pp. 40.309^0.314. 

16. Cohen, J. A Coefficient of Agreement for Nominal Scales. Educ. 
and Psychol. Meas., v. 20, No. 1, 1960, pp. 37^6. 

17. Ramsey, J. D., C. L. Burford, and M. Y. Berhir. Systematic 
Classification of Unsafe Worker Behavior. Int. J. Ind. Ergonomics, v. 1, 
1986, pp. 21-28. 



18. Richardson, W. J., and E. S. Pape. Work Sampling. Ch in Hand- 
book of Industrial Engineering, ed. by G. Salvendy. Wiley, 1984, 
pp. 4.6.1^.6.21. 

19. Silverstein, B. A. Patterns of Cumulative Trauma Disorders in 
Industry. Eng. Summer Conf. in Occup. Ergonomics, Univ. MI, Ann 
Arbor, MI, 1987, 10 pp. 

20. Hopkins, B. L., R J. Conard, and M. J. Smith. Effective and 
Reliable Behavioral Control Technology. Am. Ind. Hyg. Assoc. J., v. 47, 
No. 12, 1986, pp. 785-791. 



12 



APPENDIX A.-SAMPLE CALCULATIONS OF RELATIVE RISK RATIOS 

Direct Behavior 

(123/0.06) 



2,050 
1,338 



= 1.5 



= 2.2 



(1,381 - 123)/(1 - 0.06) 

Access Systems 

(286/0.108) 2,648 

(1,381 - 286)/(1.0 - 0.108) ™ 1,228 

Direct Behavior Accidents With Overlap Removed 

(105/0.06) 1,750 

(1,381 - 105)/(1 - 0.06) : 1,357 

Access System Accidents With Overlap Removed 

(268/0.108) 2,481 



(1,381 - 268)/(1.0 - 0.108) 1,248 



= 2.0 



Individual Access System Elements 
Ladders: 



(160/0.019) 



(1,381 - 160)/(1.0 - 0.019) 

Stairs and Steps: 

(114/0.035) 

(1,381 - 114)/(1.0 - 0.035) 

Walkways: 

(12/0.054) 



8,421 
1,245 



3,257 
1,313 



222 



= 6.8 



= 2.5 



(1,381 - 12)/(1.0 - 0.054) 1,447 



= 0.2 



13 

APPENDIX B.-CALCULATION OF PROBABILITY OF SLIP-AND-FALL ACCIDENT 
HAPPENING TO INDIVIDUAL DURING 40-YEAR PERIOD 

The probability that an individual will experience a slip- n years without a slip-and-fall accident is 0.981 raised to 

and-fall accident during any year is 0.019. Thus, the prob- the nth power. The probability of working 40 years with- 

ability that a slip-and-fall accident will not happen is out a slip-and-fall accident is thus 0.981 raised to the 

1 - 0.019 = 0.981. Each year is assumed to be indepen- 40th power, or 0.46. 
dent of every other year. The probability of working 



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